A major goal of the human genome project is identification of the complete set of human genes. Single-pass, partial sequencing of cDNA clones to generate ESTs provides a rapid and cost-effective method of gene discovery. At the same time, sequence information contained within ESTs provides a key resource for gene mapping. Understanding the function of newly identified human genes requires the increased use of model organisms that can be genetically manipulated. The generation of ESTs from model organisms and comparative genome mapping of these ESTs can also be exploited for human disease gene hunting, as well as investigating the large-scale structure and organization of the genome. The rat is an important experimental model for studying the genetic basis of many human diseases and a wide array of genetically bred rat strains with disease characteristics are available. Hence, it would be beneficial to generate an EST catalog and unique gene index of The rat genome. This application proposes the following specific aims: (1) Generate a rat EST catalog (REST) by randomly sampling cDNA clones from normalized rat cDNA libraries of different tissues. (2) Construct non- normalized full-length rat cDNA libraries and employ micro array technology.